SOURCE

<div class="outer">
    <div class="inner"></div>
    <div class="inner"></div>
    <div class="inner">123</div>
</div>

.outer{
    width: 500px;
    height:500px;
    background-color: pink;
    display:flex;
    flex-direction: column;
    align-items: flex-end;
}

.inner{
    width:100px;
    height:100px;
    background-color: yellow;
}
.inner:nth-last-child(1){
    align-self: flex-start;
    background: rgba(0, 0, 225,0.5);
}